At 25 weeks, a baby measures about 13.6 inches (34.6 cm) from head to rump and weighs roughly 1.5 pounds (660 grams), comparable in size to a large ear of corn. The baby looks distinctly human at this stage, with fully formed facial features, visible fingernails, and skin that is growing smoother as fat deposits build up underneath.
Size and Proportions
The 1.5-pound weight at 25 weeks represents a major growth spurt. Just a few weeks earlier, the baby weighed under a pound. From here, weight gain accelerates quickly as the body starts storing fat. The head is still proportionally large compared to the rest of the body, but the limbs have lengthened significantly and the torso is filling out. If you could hold a 25-week baby in your hands, it would fit comfortably across both palms.
Skin and Body Fat
One of the biggest visual changes happening around 25 weeks is in the skin. Earlier in pregnancy, fetal skin is almost translucent, with blood vessels clearly visible underneath. By 25 weeks, the baby is putting on more fat beneath the skin, which makes it appear smoother and less wrinkled. The skin still looks reddish or pinkish because there isn’t enough fat yet to fully mask the blood vessels beneath, but it’s noticeably less see-through than it was even a couple of weeks ago.
A waxy, white coating called vernix covers much of the skin at this stage. This coating protects the baby’s skin from the amniotic fluid and will gradually thin out before birth. Fine, soft hair called lanugo also covers parts of the body, helping the vernix stick to the skin. Most of this hair disappears before a full-term delivery.
Facial Features and Hair
By 25 weeks, the baby’s face looks remarkably like it will at birth. The nostrils, which were previously sealed shut, are beginning to open. Eyelids have fully formed and can open and close. The eyebrows are visible, and hair is growing on the scalp, though the amount varies widely from baby to baby. The ears have taken their final shape and are positioned where they’ll be at birth. If you were to see a 3D ultrasound at this stage, you could make out distinct features like the shape of the nose and the curve of the lips.
Movement and Behavior
A 25-week baby is active. You can feel kicks, punches, rolls, and hiccups, and many parents notice these movements becoming stronger and more predictable around this time. The baby cycles between periods of activity and rest, though these aren’t yet the organized sleep-wake patterns that develop later in pregnancy. Research shows that fetal activity tends to be higher during the daytime and lower at night, loosely syncing with the mother’s own rhythms. This preference for nighttime rest becomes more pronounced as pregnancy progresses, with older fetuses showing roughly twice the difference in daytime versus nighttime activity compared to younger ones.
The baby also responds to outside stimuli. Loud sounds can trigger a startle response, and the baby may shift position when you change yours. Some research has found that babies are more active when the mother is lying on her side compared to lying on her back.
Lung Development
The lungs are one of the last major organs to mature, and at 25 weeks they are in a critical phase of development. The airways are branching into smaller and smaller passages, and the cells lining them are beginning to specialize. Around 24 weeks, the lung cells that produce surfactant (a slippery substance that keeps the tiny air sacs from collapsing) start appearing. At 25 weeks, surfactant production is underway but still limited. This is the main reason premature babies at this age often need breathing support: there simply isn’t enough surfactant yet to keep the lungs inflating on their own. Full surfactant production ramps up significantly over the coming weeks.
Brain and Nervous System
The brain is developing rapidly at 25 weeks. The surface of the brain, which was previously smooth, is beginning to form the folds and grooves that characterize a mature brain. Nerve cells are making new connections at a tremendous rate.
A process called myelination, where nerve fibers get coated with an insulating layer that helps signals travel faster, is actively underway. This process starts in the brainstem and spinal cord around 20 to 24 weeks and continues well after birth. At 25 weeks, the insulation is still in its early stages in most parts of the nervous system, which means the baby can sense touch and respond to stimuli, but the fine-tuning of these responses will take months to complete. Some nerve pathways, particularly those connecting the brain to the muscles of the arms and legs, won’t be fully insulated even at full term.
Viability Outside the Womb
A baby born at 25 weeks is extremely premature but has a meaningful chance of survival. With intensive medical care, roughly 80% of babies born at 25 to 26 weeks survive. These babies typically need weeks or months in a neonatal intensive care unit, with support for breathing, temperature regulation, and feeding. The biggest challenges are immature lungs, difficulty maintaining body temperature due to low body fat, and vulnerability to infection. Babies born at this stage often weigh between 1 and 2 pounds and look strikingly small and thin, with reddish, somewhat translucent skin and minimal body fat.
Despite their fragility, 25-week babies can open their eyes, grasp a finger, and respond to sound and light. Their overall appearance at birth closely matches what an ultrasound would show in the womb: a tiny, fully formed baby with delicate features and limbs that move with surprising energy.